Mechanism of Improved Ductility of 1500 MPa-class Ultra-high Strength Cold-rolled Steel Sheet Produced by Rolling and Partitioning Method

By using a steel with standardized chemical composition and conventional manufacturing processes for flat-rolled steel strip, a 1500 MPa class stainless steel sheet, whose product of yield strength (YS) and total elongation (El) exceeds 30000 MPa%, was developed and its mass production was establish...

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Bibliographic Details
Published inISIJ International Vol. 60; no. 9; pp. 2097 - 2106
Main Authors Hosoya, Yoshihiro, Matsumura, Yuta, Tomota, Yo, Onuki, Yusuke, Harjo, Stefanus
Format Journal Article
LanguageEnglish
Published The Iron and Steel Institute of Japan 15.09.2020
Subjects
advanced high strength steel
Lüders strain
nanoindentation
neutron diffraction
Rolling and Partitioning method
stainless steel
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Summary:By using a steel with standardized chemical composition and conventional manufacturing processes for flat-rolled steel strip, a 1500 MPa class stainless steel sheet, whose product of yield strength (YS) and total elongation (El) exceeds 30000 MPa%, was developed and its mass production was established. Besides the excellent YS–El balance, the developed steel sheet has excellent performance for not only an anti-secondary work embrittlement but also high cycle fatigue endurance.Core technology of the developed method is composed of a combination of high precision cold-rolling and isothermal partitioning treatment in a batch furnace, named as a rolling and partitioning (R&P) method. By the R&P method, the microstructure of steel is controlled to the mixture of a strain-induced martensite as the matrix phase, and an optimum amount of retained austenite as the second phase which is dispersed in isolation and surrounded by the transformed martensite.In this paper, the microstructure formation during the R&P process and the deformation mechanism that would bring about the excellent strength–ductility balance are discussed based on the results obtained from the in situ neutron diffraction measurement. The results have revealed that the typical Lüders-like stress–strain curve of R&P steel is caused by competitive plastic flow between austenite and martensite, and an effective transformation induced plasticity phenomenon.
ISSN:0915-1559
1347-5460
DOI:10.2355/isijinternational.ISIJINT-2020-027